The oil-rich Gulf nation will also send emergency aid including medical equipment and medicines to Hamas-controlled Gaza, it said.
Qatari ruler Sheikh Hamad bin Khalifa al-Thani made the decision on a visit to Cairo to meet President Mohamed Morsi to discuss the Gaza crisis, it said.
Morsi, an Islamist linked to Hamas through the Muslim Brotherhood, sent his Prime Minister Hisham Qandil to Gaza on Friday on a visit to show solidarity with the Palestinian territory.
Qatar, which supported the uprisings in Arab Spring countries that gave power to Islamist movements last year, said in October it would invest $400 million in rebuilding Gaza.
Gaza was devastated by Israel's Operation Cast Lead offensive in December 2008 and January 2009, which claimed the lives of 1,400 Palestinians and 13 Israelis.
The investment announcement was made on a visit by the emir, the first by a head of state to Gaza since Hamas took control of it in 2007.
Israeli air strikes in the territory killed 10 people on Saturday, raising the total number of Palestinians killed to 40 in just over 72 hours of bombardment that began on Wednesday, according to Gaza's emergency services.
A further 393 Palestinians have been injured, they said.
In the same period, three Israelis have been killed by rocket fire from Gaza and another 18 injured, 10 of them soldiers, police and the army said.